Investigation of Properties of As x Se1−x Thin Films for Direct Conversion

Abstract

The electrical characteristics of metal/AsxSe1−x/metal structures for potential use in direct-conversion x-ray detectors and imaging applications are reported. The structures exhibit current rectification in both solid (amorphous, crystalline) and liquid AsxSe1−x phases. Capacitance–voltage measurements of the device in the amorphous phase find that the capacitance is essentially independent of bias. Transport phenomenon in the amorphous phase of the film was found to be influenced by trapping and the space-charge effect. In the liquid and crystalline phases, transport in the devices was characteristic of thermionic emission. The indium tin oxide (ITO)/a-As0.01Se0.99/Au 2.85-μm-thick device gave a short-circuit current (Isc) of 0.16 μA, an open-circuit voltage (Voc) of 0.1 V, and a fill factor of 0.29 at 384 K under irradiation from visible light. An interpretation of the current–voltage characteristics in the amorphous phase has been made using the self-consistent drift–diffusion model of transport, and material parameters of a-AsxSe1−x films have been extracted by fitting the experimentally measured I–V data. The model indicated that transport in the ITO/a-As0.01Se0.99/Au film was dominated by shallow-level traps with density of 5 × 1015 cm−3 at depth of 0.3 eV from the band edge. The photoconversion efficiency was found to be limited by low photogeneration efficiency, high amount of recombination losses, and the level of charge injection in the a-AsxSe1−x films.